Internet DRAFT - draft-chen-bier-anycast-label
draft-chen-bier-anycast-label
Network Working Group S. Chen
Internet-Draft F. Duan
Intended status: Standards Track Huawei Technologies
Expires: 8 May 2024 5 November 2023
BIER Anycast MPLS Label
draft-chen-bier-anycast-label-00
Abstract
This document provides a method to reduce packet loss when failures
occur at BIER transit or egress nodes or link.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 8 May 2024.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Egress Protection . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Anycast and Bypass MPLS Label . . . . . . . . . . . . . . 3
3.2. Advertisement of MPLS Label . . . . . . . . . . . . . . . 4
3.3. Establishment of BIER Forwarding Table . . . . . . . . . 4
3.4. Fast Recovery . . . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
7. Normative References . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
When failures occur at transit or egress BIER node, there is no fast
recovery or protecting mechanism currently. The recovery duration
depends on how fast the unicast algorithm can re-calculate the new
path. The new available path can only be generated in this way
called 'hard convergence'. In this document, a fast failover method
is designed for BIER to generate an alternative path for flow in
advance by allocating and transmitting additional BIER MPLS label.
In [RFC8279], BIER MPLS label was assigned locally to identify
different set of [Sub-domain, SI, BSL] and therefore can identify
different instances of BIER Forwarding Table. In this document, a
BFR node will be assigned two MPLS Labels called 'Anycast' and
'Bypass' MPLS Label. Anycast MPLS Label will be used to represent
the site, while bypass MPLS label will only be used within each site
to ensure the forwarding function.
The BIER Forwarding Table will also be modified to record two
different out interfaces for single target BFR-id.
2. Terminology
The terminology used in this document is the terminology defined
in[RFC8279], [RFC8296] and [RFC8556].
For convenience of description, the abbreviations used in this
document is listed below.
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BIER: Bit Index Explicit Replication
BGP: Border Gateway Protocol
IGP: Interior gateway protocol
BFR: Bit-Forwarding Router
BFR-ID: Bit-Forwarding Router ID
BFR-Prefix: Bit-Forwarding Router Prefix
BFR-NBR: Bit-Forwarding Router Neighbor
BIRT: Bit index routing table
BIFT: Bit index forwarding table
F-BM: Forwarding Bit Mask
MPLS: Multiprotocol Label Switching
3. Egress Protection
3.1. Anycast and Bypass MPLS Label
As shown in the following figure, one customer device is multihomed
to two BFERs in order to perform egress protection. Two BFERs are
deployed in the same egress site. Different BFR-ids and BFR-prefixes
are configured. However, they are assigned with same Anycast MPLS
label and different Bypass MPLS labels. The same Anycast label can
be used to specify the egress site. The Bypass MPLS label works as
the traditional MPLS label to ensure the normal behavior of BIER
forwarding function within the site. They are advertised by BIER-
Info Sub-Tlv in BIER prefix. BIER prefix carrying Anycast MPLS label
is called Anycast BIER Prefix. After receiving BIER prefix, BIER
MPLS Label will be contained in BIER Forwarding Table to instruct
forwarding data packet.
( BFIR-A ) ------ ( BFR-B ) ------ ( BFER-C ) ---- ( CE )
1 (0:001) \ 2 (0:010) /
\ | /
\ | /
\ | /
\ | /
( BFER-D )
3 (0:100)
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Figure 1: BIER Egress Site Deployment
3.2. Advertisement of MPLS Label
[RFC8401] defines BIER Info Sub-TLV to advertise BIER parameters such
as BFR-id, subdomain-id. The key field of the Sub-TLV is BIER
prefix. Within the Sub-TLV, sub-sub-TLV is contained and it carries
MAX-SI, BSL and MPLS Label. The sub-sub-TLV is modified in this
document so that both MPLS Labels can be advertised.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max SI | BSL | (Bypass) Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max SI | BSL | Anycast Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: New BIER Sub-sub-TLV
3.3. Establishment of BIER Forwarding Table
After receiving BIER Info Sub-TLV, BFR will parse Bypass MPLS Label
and Anycast MPLS Label. The relationship of [BFR-id, Anycast Label,
Bypass Label] will be maintained by each BFR. As shown in the figure
below, BFR will receive BIER Info Sub-TLVs from BFER-C and BFER-D.
The Anycast Label of two BFERs are different with BFR's, but they are
same with each other. BFR will combine BFR-id of BFER-C and BFER-D
as the one entry in the Bit Index Forwarding Table. Both BFER-C and
BFER-D may receive packet.
Site1 Site2
------ BFER-C ------ CE
| | |
BFR-B ---- BFER-D --------
Figure 3: BIER Egress Site Deployment
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BFR-B BIFT
--------------------------------------
| F-BM | BFR-NBR | NBR-Label |
=====================================
| 001 | A | Label-1 |
-------------------------------------
| 011 | C | AnycastLabel-2 |
-------------------------------------
| D | AnycastLabel-2 |
-------------------------------------
Figure 4: BFR-B BIFT
When BFR receives BIER data packet, it will locate the BIFT according
to the BIFT-id encapsulted in BIER header. If the packet needs to be
forwarded to BFR-id 3, it will modify the BIFT-id field as
AnycastLabel-2 and then forward it. When BFER-D receives this
packet, the packet will be finnaly sent to CE.
BFERs will also advertise their BIER Info Sub-Tlv to each other.
When BFER-C receives BFER-D's Sub-sub-TLV, it finds BFER-D has same
anycast label and different bypass label, it will encode bypass label
into its BIFT as shown below.
BFR-C BIFT
--------------------------------------
| F-BM | BFR-NBR | NBR-Label |
=====================================
| 001 | B | Label-3 |
-------------------------------------
| 100 | D | BypassLabel-13 |
-------------------------------------
Figure 5: BFR-C BIFT
3.4. Fast Recovery
When link between BFR-B and BFER-D goes down due to certain reason,
BFR-B will detect it and forward packet to BFER-C immediately
according to BIFT entry. AnycastLabel-2 will be encapsulated. When
BFER-C receives this packet, it will firstly use anycast label to
locate corresponding BIFT table. Then it will use BFR-id 3 to look
for F-BM and find its neighbor is BFER-D. The bypass label of BFER-D
will be encapsulated into data packet header. Then BFER-D will
finally receive the packet. No packet will be dropped because the
backup out interface has been generated when the anycast and bypass
MPLS Labels have been advertised and utilized.
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4. Security Considerations
//TODO
5. IANA Considerations
//TODO
6. Acknowledgements
//TODO
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>.
[RFC8296] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
for Bit Index Explicit Replication (BIER) in MPLS and Non-
MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
2018, <https://www.rfc-editor.org/info/rfc8296>.
[RFC8401] Ginsberg, L., Ed., Przygienda, T., Aldrin, S., and Z.
Zhang, "Bit Index Explicit Replication (BIER) Support via
IS-IS", RFC 8401, DOI 10.17487/RFC8401, June 2018,
<https://www.rfc-editor.org/info/rfc8401>.
[RFC8556] Rosen, E., Ed., Sivakumar, M., Przygienda, T., Aldrin, S.,
and A. Dolganow, "Multicast VPN Using Bit Index Explicit
Replication (BIER)", RFC 8556, DOI 10.17487/RFC8556, April
2019, <https://www.rfc-editor.org/info/rfc8556>.
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Authors' Addresses
Siyu Chen
Huawei Technologies
Email: chensiyu27@huawei.com
Fanghong Duan
Huawei Technologies
Email: duanfanghong@huawei.com
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